Hi
I have a filter circuit but I can not understand what kind of filter is it?!!(BESSEL or BUTTER WORTH or CHEBYSHEV,...)
could you help me please?
thanx

 

You can look the following links:

A unity-gain low-pass filter implemented with a Sallen–Key topology
http://en.wikipedia.org/wiki/Sallen–Key_topology

Sallen-Key Low-Pass Filter
http://www.ecircuitcenter.com/Circuits/opsalkey1/opsalkey1.htm